Title:
Effects of Antiwashout Admixtures on Properties of Hardened Concrete
Author(s):
Kamal Henri Khayat
Publication:
Materials Journal
Volume:
93
Issue:
2
Appears on pages(s):
134-146
Keywords:
admixtures; electron microscopes; permeability; porosity; stiffness; strength; viscosity; Materials Research
DOI:
10.14359/1412
Date:
3/1/1996
Abstract:
The effects of incorporating two commonly used types of antiwashout admixtures (AWA), welan gum and hydroxypropyl methyl cellulose (HPMC), on properties of hardened concrete are investigated for mixtures with water-cement ratios (w/c) ranging between 0.30 and 0.60. Compressive strength, flexural strength, and modulus of elasticity development up to 3 months, as well as bond with reinforcing steel, chloride ion permeability, and pore size distribution are evaluated. Test results indicate that concretes incorporating welan gum can develop 90 ¦ 10 percent compressive strength and 90 percent flexural strength of corresponding values of similar mixtures made without any AWA. For mixtures made with HPMC, these values were approximately 85 ¦ 10 percent and 92 ¦ 8 percent. The moduli of elasticity of AWA concretes made with 0.60 and 0.45 w/c can be 92 ¦ 8 percent and 85 ¦ 5 percent, respectively, of those of control mixtures. The slightly adverse effect of AWA on mechanical properties can be partially due to the additional air entrapment in the relatively fluid yet viscous concrete, as well as the increase in volume of large capillary pores. In low w/c systems, the use of AWA seems to reduce the degree of cement hydration. On the other hand, the incorporation of AWA can significantly decrease the top bar effect in fluid concrete and reduce chloride ion permeability by up to 40 percent. This is believed to be due to the improvement of the interface bond between cement paste and reinforcing bars and aggregate in the cohesive yet fluid AWA concrete.